The proposed research project is to develop sensitive methods of structural and quantitative analysis of the classes and component molecular species of naturally occurring phospholipids. Gas chromatography and combined gas chromatography-mass spectrometry were chosen as the primary analytical methods for these investigations due to the sensitivity and specificity of these techniques. These techniques developed will be applied in a study of the phospholipids normally found in the peritoneal mast cell (rat). Further studies will then be carried out to evaluate the changes in the phospholipid profiles (molecular species of various lipid classes) after treatment with various pharmacologic agents, immunological sensitization in vivo with IgE, and immunological challenge in vitro with appropriate antigen. Further studies will be carried out to elucidate the chemical structure of slow reacting substance of anaphylaxis (SRS-A). These studies involve further purification of the biological fractions (active SRS-A) from rat peritoneal cavity and separation from known contaminants. Various types of mass spectrometry will be used on untreated SRS-A as well as samples which have been subjected to degradation and derivatization to make the components of SRS-A amenable to mass spectrometry.